Typical application scenarios of UAV communications in urban areas, such as cargo delivery, traffic monitoring, and so on, their communication links are often blocked by tall building, which leads to severe degradation of channel quality. Fortunately, with its low power consumption and lightweight, the RIS can be installed at an appropriate location to reconfigure the propagation environment of air-ground links, thereby improving communication performance. Therefore, several works have studied various RIS-assisted UAV communication systems. In general, these studies fall into two categories, one for terrestrial RIS[1]}, [2]}, [3]}, [4]} and one for aerial RIS[5]}, [6]}, [7]}, [8]}, [9]}. For the first category, the UAV trajectory and the phase shift of the RIS mounted on the building surface are jointly designed to intensify different utilities such as communication coverage [1]}, energy efficiency [2]}, confidentiality [3]}, and communication rates[4]}.
